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HomeHomeDiscussionsDiscussionsiFly Wish-ListiFly Wish-ListGlide Distance CircleGlide Distance Circle
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2/11/2012 2:03 PM
 

Some aviation GPS units display a glide distance circle, indicating how far the airplane can glide at best glide speed before encountering terrain. Glide ratio would, of course, be an input.


Jeff Carter

"Now go away or I shall taunt you a second time!"

Monty Python and the Holy Grail

 
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2/14/2012 10:34 PM
 

How do those GPS's account for wind? Or does the pilot need to factor that in himself/herself?

 
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2/15/2012 10:52 AM
 

Request noted. Wind usually not accounted for in features like this, so you gotta take it with a grain of salt.

-Walter


Walter Boyd
President, Adventure Pilot
 
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2/16/2012 10:52 AM
 
Walter Boyd wrote:

Request noted. Wind usually not accounted for in features like this, so you gotta take it with a grain of salt.

-Walter


Just a quick thought....or two....

Is there a way to use the wind input from ADS-B and interpolate to generate a more accurate range and skew the circle accordingly? Probably a bit complex to program but could be a lifesaver should the unfortuate occur.

-or-

Another way which might be easier (though less accurate) could be to use the aircrafts GPS ground speed, bearing, and track data vs our inputted data for KTAS (Est Speed from flight planning page). Since we all fly as fast as we can :-) one could assume KTAS as a constant and calculate (GS actual vs KTAS) to get the aproximate real-time effects of wind. Apply the results to the inputted data for best glide speed (new data field on flight planning page)....mix in a math wiz or two to figure out the mathematical assumptions (including bearing and track data) needed to further enhance the accuracy of the range for a relative direction of flight at the assumed glide speed. This would generate whatever shape (not a circle unless no wind) that would instantly give you a very good guestimate of which way will buy you the most time / airport in range. I think this is easier to program and it would be available to all iFly owners without the need for an ADS-B receiver.
Im no engineer and I am sure there are flaws in this concept but its a start.......

Without some sort of relevance to wind it would not make much sense to include this feature since the data would be virtually worthless. Every POH gives glide data so its easy to determine how far you can glide without wind per 1k feet of altitude. Pop up the existing range circles and you can quickly see what might work. Its interpreting the wind and its effect on your range thats a biggie.

this all gives me another thought.....new wish list item posted shortly....

Dave K
 
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2/16/2012 11:55 AM
 

You really need heading + airspeed to determine wind; presuming just airpseed won't be enough. EG, if ground speed is 100 and est. speed is 120, does that mean a 20 knot head wind or a 40 knot cross-wind?

On the other hand, taking ground speed and bearing, a pilot-defined glide ratio, and terrain elevation, you can deduce when you will encounter the ground ahead of you. If winds are significant, any turn will cause an immedieate change to ground speed - thus changing the forward projected distance ground. So, perhaps a forward-only glide distance would be better than a projected glide circle.

This would require the pilot to use reason to determine if the glide distance might improve or worsen with a turn around: Is terrain higher or lower behind? Is wind from fore or aft? Etc. It would also presume the pilot's airspeed is best-glide...another big IF.

Using ADSB provided winds-aloft info is a good idea, but those reporting stations are spaced pretty far apart. But still better than guessing..

Walter


Walter Boyd
President, Adventure Pilot
 
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